The present invention relates generally to magnetic storage systems, and more particularly to storage of magnetic data in a high density format.
With the advent of the proliferation of the computer industry there has been a need for more accurate and higher density storage of information. A prior means of storage of information in a magnetic format has been on magnetic disks on both hard disks and floppy disks. Information was typically recorded on these disks on circular recording tracks in the horizontal plane of the disk. In order to both store and retrieve the information, it was necessary to locate the position of the information on the disk and align the magnetic transducer head to read and write the information in the appropriate location. A conventional method utilized for storing magnetic data comprised the use of circular guiding tracks which were recorded on the magnetic disk which provided locational information and data information stored on the disk. An external servo mechanical positioning device was utilized to position the read/write head in accordance with information provided by the locational guiding track.
A disadvantage of such a magnetic storage system is that a large percentage of each side of the disk is dedicated solely to recording guiding tracks or sectors within tracks and cannot be used to store magnetic data information. Additionally, the mechanical link between the transducer head used for transducing magnetic data and the transducer head used for transducing guidance track information is typically insufficient to align the two transducer heads in a manner which will provide sufficient accuracy to allow storage of information in a high density format on the disk. Additionally, such systems have a slow response time due to the calculations required to locate the read/write head in the proper location. Physical separation of the guidance track transducer head and the magnetic data transducer head increases propagation time which further increases the response time in the system. Also, positioning accuracy is limited by the external servo mechanism used to locate the magnetic data transducer head due to the physical limitations of the mass and inertia of the system. This further reduces the accuracy and, consequently, the density in which magnetic data can be stored on a disk.
These disadvantages and limitations were overcome to some extent by the use of guidance or control tracks which are disposed on the same side of the disk on which magnetic data is stored. Using these systems, magnetic data can be stored on both sides of the disk to increase the total amount of information storage.
The disadvantage of these systems, however, is that the useful data capacity of the disk is still diminished to some extent by the storage of locational information on a guidance track and the total amount of stored information is limited. Furthermore, such systems are expensive in that the amount of electronic circuitry required for storing positional information is considerable.
Other methods have also been used for storing position information which have not operated with suitable reliability. For example, U.S. Pat. No. 3,753,252 describes a system whereby the track position is identified by magnetic and non-magnetic regions. To provide non-magnetic regions on the surface of the magnetic layer, an acid is allowed to effect selected regions. Again, useful data capacity is lost by the recording of locational information on a disk and the total amount of stored information is limited.
U.S. Pat. No. 3,541,270 describes a magnetic head with two air gaps in juxtaposition, magnetically insulated from one another, both extending perpendicular to the direction of the track. The signals read by each head from one half of the data bearing track are compared with one another and generate a signal for correcting the position of the magnetic head if the latter deviates from the predetermined track position. A disadvantage of this device is that transducer position control is not possible during recording. This means that known positioning methods must be used in addition to that disclosed in the patent. Irregularities in the recording medium which cause signal amplitude loss or signal fluctuations may lead to faulty positioning of the transducer.
U.S. Pat. No. 4,157,576 discloses a system which utilizes a magnetic transducer with a first air gap to transduce the data track and a second air gap to detect a reference track. The reference track comprises a transition line on the recording medium between regions of a varying magnetization. Correction signals are produced in the device by sensing the location of the transition point. This system overcomes the disadvantages of prior art systems by eliminating the physical space required for recording the guidance tracks on the magnetic disk. However, precise positioning of the magnetic data transducer head, as in other prior art devices, is limited by the accuracy of the external servo system and the ability of the air gap to sense the precise location of the transition point on the disk. As in other prior art systems, response time of the system is limited by the propagation time and the time required to form the necessary calculations to properly locate the magnetic data transducer head. The sheer mass of the system and inertia associated therewith limits the positional accuracy of the magnetic data transducer head so as to limit the density of magnetic data which can be stored on the disk.